Joint for well drilling apparatus



JOINT FOR WELL DRILLING APPARATUS Filed April 2, 1965 2 Sheets-Sheet 1 FIG./

INVENTORS:

HEINZ HOERTER M/allad fi their A TTORNEY FRANZ JUSEF KNIEKELMANN Nov. 28, 1967 FR ANZnJOSEF KNICKELMANN ETAL 3,355,188

JOINT FOR WELL DRILLING APPARATUS 2 Sheets-Sheet 2 Filed April 73, 1965 CL N E I E N R J 2 M I- E rruu lheir A TTORNEY United States Patent 3,355,188 JGINT FOR WELL DRILLING APPARATUS Franz-Josef Knickelmann, Graf-Salm-Str. 31, Bedburg, Germany, and Heinz Hoerter, Mittelstr. 12, Sindorf, Kreis, Bergheim, Germany Filed Apr. 2, 1965, Ser. No. 444,997 Claims priority, application Germany, Apr. 3, 1964, R 37,607 12 Claims. (til. 28513) ABSTRACT OF THE DISCLOSURE An inner sleeve is provided rigid with one end of a rotary drill pipe, and an outer sleeve is provided rigid with one end of a tube and surrounding the inner sleeve so that the sleeves define between themselves a narrow annular gap communicating with the interior of the pipe and tube, and further define a relatively large passage communicating with the gap so that such portions of the stream of drilling mud flowing through the pipe and the tube as escaped through the gap, are free to issue from the gap through said passage.

The present invention relates to well drilling apparatus which operate in accordance with the rotary-tool method. More particularly, the invention relates to well drilling apparatus of the type preferably comprising an air lift drilling unit or a jet pumping drilling unit. Still more particularly, the invention relates to an improved joint between rotary and non-rotatable parts in such apparatus.

In well drilling apparatus to which the present invention pertains, a stream of drilling mud flows up or down through a string of drill pipe and through a non-rotatable tube which must be sealingly coupled to a section of drill pipe to prevent uncontrolled escape of mud. The heretofore used couplings or joints between such relatively movable parts are quite complicated and comprise costly sealing elements normally including packings of hardened metal and/or non-metallic hat-type packings. All such sealing elements are subjected to consider able wear because their material comes in actual contact with drilling mud which contains various corrosive and abrasive substances. Therefore, the joint between the rotary and non-rotatable parts must be inspected, repaired and its sealing elements replaced at frequent intervals.

Accordingly, it is an important object of the present invention to provide an improved joint or coupling which is constructed and assembled in such a way that it fully avoids the drawbacks of conventional joints and allows for free rotation of the drill pipe with reference to such tubular part or parts which must convey drilling mud into or from the top section of the drill pipe.

Another object of the invention is to provide a joint of the just outlined characteristics wherein the wear on sealing elements is negligible, wherein certain sealing elements need not come in actual contact with drilling mud, and wherein any such mud which happens to escape between the relatively movable parts of the joint may be collected and recirculated in a simple way.

A further object of the invention is to provide a novel connection between the rotary and non-rotatable mudconveying parts at the upper end of a string of drill pipe.

An additional object of the present invention is to provide a joint which can be readily taken apart and reassembled, wherein the solid fraction which forms part of drilling mud is not likely to prevent rotation of the drill pipe, and wherein any solid particulate matter which happens to penetrate between the rotary and non-rotatable parts is automatically expelled in response to continued flow of mud through the drill pipe.

Still another object of the invention is to provide a well drilling apparatus which embodies a joint of the above outlined characteristics.

A concomitant object of the invention is to provide a well drilling apparatus which embodies the improved joint and wherein a stream of mud flows upwardly through the drill pipe to be recirculated through the well bore.

Briefly stated, one feature of our invention resides in the provision of a well drilling apparatus which comprises a non-rotatable tube, a string of rotary drill pipe movable up and down to descend into or to be withdrawn from a well bore, and a novel joint between the top section of the drill pipe and the tube. The joint comprises a rotary inner sleeve which is sealingly secured (e.g., by welding) to the top section of the drill pipe and one end portion of which is adjacent to but spaced from the lower end of the tube, an outer sleeve which is sealingly secured (e.g., by welding) to the lower end of the tube and surrounds and is supported by the inner sleeve, a first wearand corrosion-resistant annular member secured to the upper end portion of the inner sleeve, and a'second wearand corrosion-resistant annular member which is mounted in the outer sleeve and is closely adjacent to the first annular member. The two sleeves and the two annular members together define a continuous relatively large passage through which a stream of drilling mud may flow from the tube into the top section of the drill pipe or vice versa. When the apparatus comprises an air lift drilling unit or a jet pumping drilling unit, a stream of drilling mud flows upwardly and is propelled by compressed gas or water which is pumped or injected into the drill pipe.

In accordance with another feature of our invention, the two annular members may define between themselves a narrow annular gap which allows some drilling mud to leak therebetween. Such mud accumulates in an annular internal chamber of the outer sleeve and is perrnitted to flow into a collecting receptacle which may be mounted on and then preferably surrounds the outer sleeve. The receptacle may be connected with a suitable return conduit which conveys the thus accumulated mud into the well bore or into a suitable pond or tank wherein the solid particulate matter settles. The remainder of mud, mainly liquid, is discharged from the pond and flows back into the well bore.

The width of the gap between the two annular members may increase gradually in a direction radially outwardly from the internal surfaces of the annular members to prevent clogging of the gap by particles of solid matter which forms part of the mud.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved joint itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of a specific embodiment with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevational View of a well drilling apparatus embodying a joint which is constructed in accordance with our invention, certain portions of the apparatus and the well bore being shown in vertical sect-ion; and

FIG. 2 is an enlarged axial section through the joint.

Referring first to FIG. 1, there is shown a well drilling apparatus which operates in accordance with the rotarytool method. This apparatus comprises a drilling rig including a boom 37 which carries a raising and lowering mechanism here shown as composed of a cable 38 trained around pulleys 36, 36a the latter of which is mounted at the upper end of the boom. The free end of the cable 38 is connected with a suitable winch, not shown, so that i the string a of drill pipe may be moved up or down. The lower end of the drill pipe 10a carries a tool here shown as a bit 1015 which removes material surrounding the lower end of the well bore 40. The boom 37 is propped by guy wires 37a (only one shown). The top section 10 of the drill pipe 10a is of polygonal or other non-circular outline and is slidably but non-rotatably received in the aperture of a rotary table 41 driven by a suitable engine 42, for example, an internal combustion engine. Thus, the table 41 can rotate to drive the drill pipe 10a, and this pipe is free to move axially with reference to the table. The table is mounted in suitable bearings, not shown, in a manner well known from the art of such drilling apparatus.

The apparatus of FIG. 1 includes a so-called air lift drilling unit according to which a compressor 34b pumps compressed air or another suitable gas through a flexible conduit 34 leading to a stationary header 34a. This header admits compressed air alternatively to one of two supply conduits 31, 32 which rotate with the drill pipe 10a and serve to admit such air into the lower part of the drill pipe. In FIG. 1, the conduits 31, 32 admit compressed gas into an intermediate section 33 which forms part of the drill pipe 10a whereby such compressed gas forces drilling mud 43 to flow upwardly through the drill pipe. A stream 44 of mud issues from a non-rotatable outlet tube 16 which communicates with the upper end of the drill pipe 10a and discharges into a settling tank or pond 39a. The lower part of the pond 39a constitutes a settling Zone and communicates with an underground channel 39 discharging into the well bore 40. The mud enters the drill pipe 10a at one or more points and is recirculated as follows: The compressor 34b pumps compressed gas through the conduit 34 and into the header 34a. This header admits compressed gas into the supply conduit 31 or 32, and such gas flows along a series of revolving sections 30 and into the intermediate section 33. The mud filling the pipe 100 is streaming upwardly and expelled through the outlet tube 16 and flows into the pond 39a where the solid matter settles. The channel 39 allows the same quantity of mud to flow back into the well bore 40. The mud penetrates into the drill pipe 10a and is again expelled by jets of compressed air which is admitted into the intermediate section 33. Such portions of the supply conduits 31, 32 which pass through the aperture of the rotary table 41 are recessed into the wall of the top section 10 so that they are free to rotate with the drill pipe 10a.

The heretofore described parts of the drilling apparatus are well known in the art and by themselves form no part of our invention. The invention is embodied in a novel coupling or joint 9 between the top section 10 of the drill pipe 10a and the outlet tube 16, and the purpose of this joint is to insure that the section 10 can rotate with reference to the outlet tube 16 while permitting the mud to flow continuously back into the pond 39a. Another important feature of the invention resides in such construction of the joint 9 that uncontrolled leakage of mud may be prevented in a very simple way. Any mud which happens to leak between the rotary and stationary parts of the joint 9 can be collected and recirculated in a very simple, inexpensive and practical manner.

It is clear that the present invention may be embodied with equal advantage in well drilling apparatus which include so-called jet pumping drilling units wherein an injector serves to accelerate the mud filling the top sect-ion 10 so that a stream of mud flows upwardly and toward the outlet tube 16. The joint 9 may be utilized in all such types of drilling apparatus which operate in accordance with the rotary-tool method and wherein a stream of mud flows upwardly, or downwardly through the upper end of the drill pipe 100.

The manner in which the header 34a admits compressed gas to the supply conduit 31 or 32 is well known and need not be described here.

Referring now to FIG. 2, it will be seen that the top section 10 of the drill pipe 10a is rigidly connected to an inner cylinder or sleeve 11 which is sealingly and coaxially secured thereto by bolts 11a or the like. Thus, the sleeve 11 shares all angular and axial movements of the drill pipe 10a. This sleeve is surrounded by an outer sleeve or cylinder 12 which is held against rotation but invariably shares all axial movements of the drill pipe 10a. The inner sleeve 11 rotates in two antifriction bearings 13 and the axial ends of the annular clearance between the sleeves 11, 12 are sealed by suitable packings 14. These packings may be of relatively simple construction because they need not come in actual contact with the mud 43.

The top portion of the outer sleeve 12 forms an annular cap or lid 15 which is coaxial with and is welded or otherwise sealingly secured to the lower end of the arcuate outlet tube 16. The parts 19, 11, 15, 16 define a continuous and relatively large passage in which a stream of drilling mud may rise in the direction indicated by arrows 21 to flow back into the pond 39a. The cap 15 preferably forms a detachable part of the outer sleeve 12 and is secured thereto by bolts 15a or by similar fasteners.

In accordance with a feature of our invention, the upper end portion of the inner sleeve 11 is rigidly connected with a lower metallic annular member or ring 17 (see the bolts 18) and its internal diameter preferably equals the internal diameter of this ring. The radially outermost portion of the ring 17 overlies the upper packing 14 and an annular rib 12a of the outer sleeve 12. The underside of the cap 15 carries a second metallic annular member or ring 19 which is secured thereto by bolts or screws 20. The internal diameter of the ring 19 equals the internal diameter of the ring 17 and outlet tube 16. The two rings define between themselves a narrow annular gap 26 through which some of the mud may leak in the direction indicated by an arrow 27, i.e., radially outwardly of the inner sleeve 11. It will be noted that the width of the gap 26 increases gradually in a direction radially outwardly to make sure that any solid particulate matter which might enter the gap 26 can be expelled in response to the pressure of drilling mud and/or gas which escapes in the direction indicated by the arrow 27. The cap 15 is formed with one or more upwardly extending ports 28 which prevent the escape of mud but allow gases to escape from an annular chamber 22 which communicates with the gap 26 and with one or more downwardly extending discharge openings 24 machined into the outer sleeve 12. The sleeve 12 is surrounded by an annular collecting receptable or trough 23 whose upper end is open so that mud leaking through the gap 26 between the rings 17, 19 and escaping through the chamber 22 may flow through the opening or openings 24 and accumulates in the receptacle 23. This receptacle communicates with a return conduit 25 which directs the mud back into the pond 39a.

The distance between the rings 17, 19 is selected in such a way that the mud leaking through the gap 26 constitutes but a small fraction of material which flows into the outlet tube 16 and back to the pond 39a (arrow 44 in FIG. 1). Each of these rings may be replaced by two or more wearand corrosion-resistant rings, as long as such rings insure that the sleeve '11 may rotate with the top section 10 while the sleeve 12 remains in a selected angular position. In other words, each ring which is attached to the inner sleeve 11 should be free to rotate with the top section 10 but the ring or rings 19 should not share such angular movement. It can be said that the rings 17, 19 respectively form part of the sleeves 1'1, 12 whereby the ring 19 is provided in the interior of the sleeve 12 just above the ring 17 which is provided at the upper end of the sleeve 11. The chamber 22 defines with the opening or openings 24 a path through which the liquid and/or gaseous matter leaking through the gap 26 can escape from the joint 9.

A very important advantage of the improved joint 9 is that the wear on its sealing elements is negligible. The packings 14 need not come into actual contact with the stream of drilling mud which flows through the drill pipe Illa and outlet tube '16, and their main function is to prevent entry of dust into the bearings 13. The outer sleeve 12 is supported solely by the outer races of the bearings 13 because the rings 17, 19 are preferably spaced from each other to define the aforementioned gap 26. In other words, we prefer to replace conventional metallic and non-metallic packings by two or more rings 17, 19 which are mounted in such a way that some drilling mud is free to leak from the joint. However, such leakage of mud is fully controlled by the provision of the path defined by the gap 26, chamber 22, opening or openings 24, recentacle 23 and return conduit 25. The wear on the rings 17, 19 is minimal because they need not come in actual contact with each other and, therefore, their exposed surfaces are subjected only to such wear which is caused by solid particulate matter escaping through the gap 26. It is clear that the rings 17, 19 may be mounted in such a way that their end faces come in actual contact with each other; in such joints, the provision of the receptacle 23 and pipe 25 may merely serve as a safety measure. Particles of sand or similar solid material which happen to enter the gap 26 are expelled by fluid flowing toward the chamber 22, and such expulsion of solid particulate matter is enhanced by the aforementioned gradual widening of the gap 26 in a direction from the interior of the inner sleeve 11 toward the chamber 22. Also, the material of the rings 17, 19 is sufliciently wear-resistant to insure that the rings comminute any such particles which tend to remain in the gap 26.

The provision of ports 28 is of particular importance when the well drilling apparatus includes an air lift drilling unit or a jet pumping drilling unit, i.e., whenever the material flowing through the gap 26 contains gaseous substances. The diameters of the ports 28 are too small to permit escape of liquid or solid matter, but they cannot prevent escape of gases so that the liquid escaping from the chamber 22 descends into the collecting receptacle 23 by gravity flow.

If the collecting receptacle 23 is omitted, drilling mud escaping from one or more openings 24 accumulates in a receptacle which need not be connected with the outer sleeve 12, or such mud is otherwise deflected and directed to flow into the well bore 40 and/ or pond 39a.

It is also clear that the improved joint may be used with equal advantage in well drilling apparatus wherein the tube 16 serves as an inlet to admit drilling mud into the inner sleeve 11 so that such mud flows downwardly through the string of drill pipe a and is discharged into the well bore 40.

The members or rings 17 and 19 can be made of any other wearand corrosion-resistant material than metal, for instance plastic.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for vari ous applications without omitting features which fairly constitute essential chracteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a well drilling apparatus, a tube having a lower end; a string of rotary drill pipe including a top section having an upper end, said drill pipe being arranged to convey a stream of drilling mud; and a joint between said tube and said drill pipe, comprising a rotary inner sleeve rigid with the upper end of said top section and having an upper end portion adjacent to but spaced from the lower end of said tube, an outer sleeve rigid with the lower end of said tube, said outer sleeve surrounding and being rotatably supported by said inner sleeve, a first ring rigid with the upper end portion of said inner sleeve, and a second ring rigidly mounted within said outer sleeve adjacent to but spaced from said first ring and defining therewith a narrow unobstructed annular gap, said outer sleeve defining a path communicating with said gap and said rings and said sleeves together forming a continuous substantially enclosed passage for enabling escape of a portion of the mud of the stream of drilling mud and for discharge of such portion from said outer sleeve.

2. In a well drilling apparatus, a tube having a lower end; a string of drill pipe including a top section having an upper end, said drill pipe being arranged to convey a stream of drilling mud; and a joint between said tube and said drill pipe, comprising a rotary inner sleeve sealingly affixed to the upper end of and rotatable with said top section, said inner sleeve having an upper end portion adjacent to but spaced from said tube, an outer sleeve sealingly afiixed to the lower end of said tube, said outer sleeve surrounding and being rotatably supported by said inner sleeve, a first wear-resistant ring mounted on the upper end portion of said inner sleeve, and a second wearresistant ring mounted in said outer sleeve and being adjacent to but spaced from said first ring so as to definetherewith a narrow annular gap, said outer sleeve having an annular chamber surrounding and communicating with said annular gap and said outer sleeve further having at least one discharge opening communicating with saidchamber, said sleeves and said rings together defining a continuous passage through which a relatively large stream of drilling mud can flow between said drill pipe and said tube whereby any such mud which happens to leak through said gap accumulates in said chamber and is discharged through said opening.

3. In a well drilling apparatus, a tube having a lower end; a string of drill pipe including a top section having an upper end, said drill pipe being arranged to convey a stream of drilling mud; and a joint between said tube and said drill pipe, comprising a rotary inner sleeve sealingly ailixed to the upper end of and rotatable with said top section, said inner sleeve having an upper end portion adjacent to but spaced from said tube, an outer sleeve sealingly affixed to the lower end of said tube, said outer sleeve surrounding and being rotatably supported by said inner sleeve, a first wear-resistant ring mounted on the upper end portion of said inner sleeve, a second wearresistant ring mounted in said outer sleeve and being adjacent to but spaced from said first ring so as to define therewith a narrow annular gap, said outer sleeve having an annular chamber surrounding and communicating with said annular gap and said outer sleeve further having at least one downwardly extending discharge opening communicating with said chamber, and a collecting receptacle externally adjacent to said outer sleeve and positioned to collect such drilling mud which escapes from said chamber, said sleeves and said rings together defining a continuous passage through which a relatively large stream of drilling mud can flow between said drill pipe and said tube whereby any such mud which happens to leak through said gap accumulates in said chamber and is discharged through said opening to enter said receptacle.

4. In a well drilling apparatus, a tube having a lower end; a string of rotary drill pipe including a top section having an upper end, said drill pipe being arranged to convey a stream of drilling mud; and a joint between said tubeand said drill pipe, comprising a rotary inner sleeve rigid with the upper end of said top section and having an upper end portion adjacent to but spaced from the lower end of said tube, an outer sleeve rigid with the lower end of said tube, said outer sleeve surrounding and being rotatably supported by said inner sleeve, a first ring rigid with the upper end portion of said inner sleeve, and a second ring rigidly mounted internally of said outer sleeve adjacent to but spaced from said first ring and defining therewith a narrow unobstructed annular gap whose width increases radially outwardly, said outer sleeve defining a path comunicating with said gap, and said rings and said sleeves together forming a continuous substantially enclosed passage for enabling escape of a portion of the mud of the stream of drilling mud and for discharge of such portion from said outer sleeve.

5. A structure as set forth in claim 4, wherein the width of said unobstructed gap increases gradually and wherein said path includes an annular chamber provided in said outer sleeve and surrounding said annular gap, said chamber being in communication with and receiving mud from said gap and said outer sleeve further having at least one discharge opening communicating with said chamber.

6. In a well drilling apparatus, a tube having a lower end; a string of drill pipe including a top section having an upper end, said drill pipe being arranged to convey a stream of gas-containing drilling mud; and a joint between said tube and said drill pipe, comprising a rotary inner sleeve sealingly affixed to the upper end of and rotatable with said top section, said inner sleeve having an upper end portion adjacent to but spaced from said tube, an outer sleeve sealingly affixed to the lower end of said tube, said outer sleeve surrounding and being rotatably supported by said inner sleeve, a first wear-resistant ring mounted on the upper end portion of said inner sleeve, and a second wear-resistant ring mounted in said outer sleeve and being adjacent to but spaced from said first ring so as to define therewith a narrow annular gap, said outer sleeve having an annular chamber surrounding and communicating with said annular gap and said outer sleeve further having at least one gas-discharging port and at least one mud-discharging opening, said port and said opening being in communication with said chamber, said sleeves and said rings together defining a continuous passage through which a relatively large stream of drilling mud can fiow between said drill pipe and said tube whereby any such mud which happens to leak through said gap accumulates in said chamber and is discharged through said opening, any gases which enter said chamber being discharged through said port.

7. A structure as set forth in claim 6, wherein said opening extends downwardly and said port extends upwardly from said chamber.

8. In a well drilling apparatus, a tube having a lower end; a string of rotary drill pipe including a top section having an upper end, said drill pipe being arranged to convey a stream of drilling mud; and a joint between said tube and said drill pipe, comprising an inner sleeve sealingly connected to the upper end of and coaxial with said top section, said inner sleeve having an upper end portion adjacent to but spaced from the lower end of said tube; an outer sleeve comprising an annular top portion sealingly secured to the lower end of and coaxial with said tube, the remainder of said sleeve forming a cylinder which surrounds and is rotatably supported by said inner sleeve, said top portion of the outer sleeve having an underside adjacent to but spaced from the upper end portion of said inner sleeve, a first ring coaxially secured to the upper end portion of said inner sleeve, and a second ring rigidly and coaxially secured to the underside of the top portion of said outer sleeve with spacing from said first ring, said rings defining between themselves a narrow unobstructed annular gap and said outer sleeve having at least one discharge opening which communicates with said gap, said sleeves and said rings together forming a relatively large substantially enclosed continuous passage through which a portion of the stream of drilling mud can flow between said drill pipe and said tube whereby such portion is free to escape through said opening.

9. As a novel article of manufacture, a joint for connecting rotary and non-rotatable liquid-conveying parts of a well drilling apparatus, particularly for connecting the top section of a rotary drill pipe to a tubular outlet, said joint comprising an inner sleeve having an end portion provided with a wear-resistant ring; an outer sleeve surrounding said inner sleeve, one of said sleeves being rotatable with reference to the other sleeve and said outer sleeve having an internally mounted wear-resistant ring adjacent to but spaced from said first named ring, said rings defining between themselves an annular gap which is narrow at least in the zone adjacent to the internal surfaces of said rings and said other sleeve defining a path including a discharge opening which communicates with said gap so that, when said sleeves convey a stream of fluid and some fiuid leaks through said gap, such leak fluid is free to escape through said opening.

10. A joint as set forth in claim 9, wherein said inner sleeve is rotatable with reference to said outer sleeve and further comprising antifriction bearing means mounted between said sleeves.

11. A joint as set forth in claim 9, wherein the width of said gap increases in a direction radially outwardly and wherein said path includes an annular chamber provided in said outer sleeve and communicating with said gap and with said opening.

12. A joint as set forth in claim 11, wherein said outer sleeve is provided with at least one gas-discharging port which communicates with said chamber.

References Cited UNITED STATES PATENTS 1,259,853 3/1918 Greve 285-l3 X 1,574,221 2/1926 Taylor 285l3 X 1,737,465 11/1929 Lindsey 28513 2,279,969 4/1942 Casperson 285l4 2,683,587 7/1954 Gunning -209 X CARL W. TOMLIN, Primary Examiner.

R. G. BERKLEY, Assistant Examiner. 

1. IN A WELL DRILLING APPARATUS, A TUBE HAVING A LOWER END; A STRING OF ROTARY DRILL PIPE INCLUDING A TOP SECTION HAVING AN UPPER END, SAID DRILL PIPE BEING ARRANGED TO CONVEY A STREAM OF DRILLING MUD; AND A JOINT BETWEEN SAID TUBE AND SAID DRILL PIPE, COMPRISING A ROTARY INNER SLEEVE RIGID WITH THE UPPER END OF SAID TOP SECTION AND HAVING AN UPPER END PORTION ADJACENT TO BUT SPACED FROM THE LOWER END OF SAID TUBE, AN OUTER SLEEVE RIGID WITH THE LOWER END OF SAID TUBE, SAID OUTER SLEEVE SURROUNDING AND BEING ROTATABLY SUPPORTED BY SAID INNER SLEEVE, A FIRST RING RIGID WITH THE UPPER END PORTION OF SAID INNER SLEEVE, AND A SECOND RING RIGIDLY MOUNTED WITHIN SAID OUTER SLEEVE ADJACENT TO BUT SPACED FROM SAID FIRST RING AND DEFINING THEREWITH A NARROW UNOBSTRUCTED ANNULAR GAP, SAID OUTER SLEEVE DEFINING A PATH COMMUNICATING WITH SAID GAP AND SAID RINGS AND SAID SLEEVES TOGETHER FORMING A CONTINUOUS SUBSTANTIALLY ENCLOSED PASSAGE FOR ENABLING ESCAPE OF A PORTION OF THE MUD OF THE STREAM OF DRILLING MUD AND FOR DISCHARGE OF SUCH PORTION FROM SAID OUTER SLEEVE. 